1991 is pre-OBD2. code readers will not work.
however, all is not lost. Many cars have an alternate way of reading codes from the computer.
Toyota has a block under the hood and you short couple wires together and count engine light flashes
Chrysler you can turn the ignition key on and off a few times and count engine light flashes
in your case for GMs from 1982 to 1995
1: find the 12 pin connector under the dash and short the upper two rightmost terminals.
with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a Code 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession.
2:. After Code 12 is displayed, any stored trouble codes will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All codes are displayed 3 times each then a code 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.
Tech -- GM 2 Digit codes for 82 and up (non OBD-II)
code - code definition
12- diagnostic mode
13- 02 sensor or circuit
14- coolant sensor or circuit/ high temp indicated
15- coolant sensor or circuit/ low temp indicated
16- system voltage out of range
19- crankshaft position sensor or circuit
21- throttle position sensor or circuit- voltage high
22- throttle position sensor or circuit- voltage low
23- mixture control (m/c) solenoid or circuit (carbureted models)
23- manifold air temperature (mat) sensor or circuit (1990 and earlier models)
23- intake air temperature (iat) sensor circuit (fuel-injected models)
24- vehicle speed sensor (vss) or circuit
25- manifold air temperature (mat) sensor or circuit - high temperature indicated (1990 and earlier models)
25- intake air temperature (iat) sensor or circuit - high temperature indicated (1991 and later models)
26- quad driver module circuit
27- quad driver module circuit
28- quad driver module circuit
29- quad driver module circuit
31- park/neutral position (pnp) switch circuit
32- baro sensor or circuit (carbureted models)
32- egr circuit (fuel-injected models)
33- manifold absolute pressure (map sensor signal voltage high
33- mass air flow (maf) sensor or circuit - excessive airflow indicated
34- manifold absolute pressure (map) sensor signal voltage low 34- mass air flow (maf) sensor signal - low airflow indicated
35- idle speed control (isc) switch or circuit (shorted) (carbureted models)
35- idle air control (iac) valve/ circuit
38- brake switch circuit
39- torque converter clutch (tcc) circuit
41- no distributor signals to ecm, or faulty ignition module ( carbed models)
41- cylinders select error- mem-cal or ecm problem ( fuel-injected models
41- cam sensor circuit (3.8 engine)
42- bypass or electronic spark timing (est) circuit
43- low voltage at ecm terminal l (carbureted models)
43- knock sensor circuit
44- oxygen sensor or circuit - lean exhaust detected
45- oxygen sensor or circuit - rich exhaust detected
46- power steering pressure switch circuit
48- misfire diagnosis
51- prom, mem-cal or ecm problem
52- calpak or ecm problem
53- egr fault (carbureted models only)
53- system over-voltage (ecm over 17.7 volts)
54- mixture control (m/c) solenoid or circuit (carbureted models)
54- fuel pump circuit (1986 and later models)
55- oxygen sensor circuit or ecm
55- fuel lean monitor (2.2l engine)
61- oxygen sensor signal faulty (possible contaminated sensor)
62- transaxle gear switch signal circuits
63- manifold absolute pressure (map) sensor voltage high (low vacuum detected)
64- manifold absolute pressure (map) sensor voltage low (high vacuum detected)
66- pressure sensor or circuit air conditioning
Hi, Anonymous the following applies to carbureted also fuel injected models and the usual suspects are:
1. Severely discharged or a damaged battery, 9 volts or lower.
2. Faulty alternator/generator and or voltage regulator.
3. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
4. Faulty main circuit breaker or ignition switch, check for loose connections and continuity.
5. Faulty system and or ignition relay, check for continuity.
6. Faulty ignition coil, ignition/electronic module.
7. Faulty CKP, CPS, CMP, MAP, TPS, O2, or BAS sensor, corroded, loose or broken wire connector pins/sockets.
8. Water or dirt in the fuel system, carburetor or filter.
9. . Restricted, blocked or kinked fuel line.
10. Fuel tank empty.
11. The gas cap is not venting properly or fuel tank venting system blocked.
12. A faulty Fuel Pump, pressure regulator and or fuel injectors.
13. Vacuum line from intake manifold to petcock broken, cracked, or not attached, carburetor vent line plugged.
14. Needle and seat stuck closed in the float bowl.
For more information about your issue, please visit the websites below.com. Good luck and have nice a day. Chinese scooter won continue to run HELP scooter wont stay running clean carb How to tune carburetor in GY6 chinese scooter 150 or 50 cc Scooter Carburetor Idle Adjust Classic Motorcycles
Hello, first is it carburetor or fuel injected engine? When was the last time it
was tuned up?
If carbureted engine then the carburetor will need to be rebuilt or replaced
with a rebuilt carb.
If fuel injected engine. low fuel pressure, faulty fuel injectors, new air
cleaner, throttle position sensor might need to be replaced, air flow sensor
could be faulty, broken vacuum hoses, plug fuel filter, faulty fuel pump, new
spark plugs, etc. All of these things need to be checked out.
You are probably not getting very good fuel mileage. Couple of things will be
needed. rebuild carburetor, new filters, and a tune up. GB...stewbison